Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 250310
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1010 PM CDT Fri Apr 24 2015

...Updated mesoscale discussion...

.MESOSCALE DISCUSSION...
Issued at 947 PM CDT FRI APR 24 2015

Large complex of thunderstorms is steadily progressing east this
evening, and will continue to do so through the early morning
hours. Currently it is moving into an airmass characterized by
500-800 J/kg of most unstable CAPE with a most unstable lifted
parcel level near 1000 m. Surface parcels are also unstable but
capped. Current radar indicates that the main cold pool is about 15
miles ahead of the convective updrafts, also indicative of the
elevated nature. Where the updrafts do develop, they are vertical
in nature although not particularly tall, likely owing to the
steep mid level lapse rates, and where stronger updrafts have
developed there have been temporary indications of low level
rotation. These have largely been limited to portions of the
bowing line angled from SE to NW which are also the areas of the
line that are most stable to surface parcels. With that in mind,
the potential for these mesovortices to translate any enhanced
enhanced wind or rotation to the surface is very low.

Will need to continue to monitor the evolution of this system,
with some interest given to the southern flank as there is
stronger deep layer shear in those areas near/southeast of Council
Grove. However, the overall airmass is expected to become
increasingly stable overnight and east central KS will be
displaced from the strongest deep layer forcing with the storm
system. So, while the convection was quite intense in central KS,
it has weakened a bit with eastward progression, and will continue
to do so through the night. There is still some potential for hail
or even a localized damaging wind gust, but for much of the night
will have a focus on beneficial rainfall and frequent lightning...
with a few areas flirting with locally excessive rainfall from
Ottawa through Washington counties.

&&

.SHORT TERM...(Through Tonight)
Issued at 138 PM CDT FRI APR 24 2015

At 2 PM, a loosely defined warm front extended from just north of
Hays and Russel to just north of Newton...and was becoming
slightly better defined as it lifted north. Meanwhile, a very dry
low level airmass over southwest Kansas was pushing east
northeast, arcing from near Pratt to the northwest. The zone in
between these two features appears to be the favored area for
convective initiation some time around 3-4 PM. Storms that develop
in this region are expected to become supercellular and track
toward the east along the northward lifting warm front. Farther
east, the local forecast area was cloud covered at 2 PM, still in
the cool sector north of the warm front. However, the front is
still expected to lift north to near I-70 by late afternoon while
surface low pressure deepens in SW to SC Kansas. Convergence will
intensify along the front late afternoon and could force
additional convection immediately along the boundary. Any storms
that develop in this manner would likely be focused west of Topeka
through 8 PM, and would seem likely to lift north of the front and
become elevated in nature. This would lend to a large hail risk
unless a storm could root and track along the front, in which case
all hazards would be possible.

Will need to closely watch both of these areas of development as
the environment this evening will be characterized by ample low
level and 0-8 km wind shear, and some storm organization is
likely. However, there are periods of weakness in the mid level
wind fields and this could complicate storm mode in addition to
the strong forcing likely initiating clusters of storms rather
than isolated cells. The current thinking is that large hail will
be the primary hazard with some possibility for pockets of
damaging wind to develop. The entire area has a non-zero tornado
potential, but it appears that the best chance for semi-discrete
supercell structures and attendant tornado/very large hail threat
will be west of Topeka and generally within 40 miles North/South
of I-70 before 10 PM. As convective mode gets messier with
competing updrafts later in the evening, the potential for very
large hail diminishes, but ample wind shear, some surface based
instability, and strong forcing keeps at least some potential
hail, wind, and even a tornado into the early morning in east
central KS.

Finally, there is some potential for a few hours of training cells
along and just north of the warm front which could result in some
localized heavy rainfall amounts or even some flash flooding.
Moisture content of the air is not spectacular though so it would
take a few storms in quick succession to cause any flooding.

Storms will come to an end from northwest to southeast overnight,
with a few lingering showers or storms in the northeast through
sunrise.

.LONG TERM...(Saturday Night through Friday)
Issued at 333 PM CDT FRI APR 24 2015

Saturday morning the mid and lower level low pressures becomes
stacked over far NE KS. Wrap around moisture in the form of showers
should make it into far NE KS on the backside of the low pressure,
and linger through the morning hours before clearing out. A decent
pressure gradient will keep the winds gusty out of the north in far
eastern KS most of Saturday. High temperatures will range from near
60 in far NE KS to the mid 70s in east central KS. Saturday night a
secondary cold front pushes more stable air and lower dew points
southward across the forecast area. That front will push well south
of the area as another closed mid level low ejects out of the
southern Rockies into the southern plains. Upper level divergence
and isentropic lift ahead of this system will bring a slight chance
for showers Sunday night into Monday across SE and portions of
central KS. During this period high temperatures will generally be
in the 60s, while low temperatures generally reach the 40s.

For the extended period into Tuesday, there may be just enough
moisture and isentropic ascent still extending into far southeastern
KS to provide enough lift to see a few showers in the outlook area.
However, this is only through the GFS solution.  The EC and others,
show a drying trend quicker and the associated low staying off to
the South before filling and becoming an open wave as it moves off
to the East.  The rest of the period should see very small chance to
no moisture as any significant energy will stay well to the North as
a strong mid to upper level ridge builds into the area.  With rising
heights, fair weather conditions should be the story through much of
the next week.  Temperatures during this time rise into the 70s with
low 80s not out of the question.  Overnight lows remain pleasant in
the upper 40s and 50s.

&&

.AVIATION...(For the 00Z TAFs through 00Z Saturday Evening)
Issued at 552 PM CDT FRI APR 24 2015

For the 00z TAFs, MVFR cigs are in place ahead of the approaching
storm system that will bring periods of showers and thunderstorms to
the TAF sites this evening through the overnight hours. IFR
conditions will be possible at times with any of the stronger storms
that track over the TAF sites, along with gusty winds. Showers with
some scattered thunderstorms should persist into Saturday morning
before exiting from west to east. Winds will shift from southeast to
northwest with this passing system.  Uncertainty lies with whether
cigs will scatter out and improve to VFR for the remainder of
Saturday or if MVFR stratus will linger behind the exiting
precipitation through the afternoon hours, so we will continue to
monitor this potential in future TAF updates.


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

MESOSCALE...Barjenbruch
SHORT TERM...Barjenbruch
LONG TERM...Drake/Sanders
AVIATION...Hennecke






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